Isobutylene-based polymer nanocomposites are used as materials of choice for tire innerliners due to their air retention properties. One example of such a nanocomposite is one comprising a functionalized poly(isobutylene-co-p-methylstyrene) elastomer and organoclay, or “layered clays” as described in US 2009-0050251. Typically, nanocomposites are made by melt mixing elastomers and clay at elevated temperature. Due to the hydrophobic and polymeric nature of butyl rubber, it is difficult to achieve a good dispersion or effective exfoliation of the clays. An earlier publication describes a novel method of making butyl rubber/clay nanocomposites, WO 2006-085957 A2. The organoclays are first treated with suitable organic solvents. The elastomer and clay, having been treated with solvents, are then blended with one another, and with exfoliating agents, to form a nanocomposite.
When such nanocomposite materials are used in innerliner compounds, a processing aid, typically naphthenic oil, is added in the innerliner formulation to ensure an adequate processing quality of the compounds. Taking advantage of the solution process for forming nanocomposites, the inventors here find a novel and beneficial way to incorporate processing aid, in the process of making nanocomposite. The resulting nanocomposite will allow a further improvement in impermeability performance by eliminating the naphthenic oils further compounding of the elastomeric nanocomposite. In addition the nanocomposites also show maintained or improved compound processability.
Publications that describe blends of elastomers and exfoliated clays include US 2004-0132894, US 2004-0194863, US 2005-0027057, US 2006-0235128, US 2007-0015853, US 2007-0219304, US 2009-0005493, and WO 2008-118174.